This present application relates to turbine engines. More specifically, but not by way of limitation, the present application relates to the circumferential positioning of airfoils in relation to the positioning of cooling air ejection ports and the flowpath of cooling air through the turbine hot gas path section of the engine.
A gas turbine engine typically includes a compressor, a combustor, and a turbine. The compressor and turbine generally include rows of airfoils or blades that are axially stacked in stages. Each stage generally includes a row of circumferentially spaced stator blades, which are fixed, and a set of circumferentially spaced rotor blades, that rotate about a central axis or shaft. While there are other types of combustors, gas turbine engines often have cylinder shaped combustors, which are often called “can combustors.” As described in more detail below, a can combustor assembly generally includes a plurality of individual “cans” that are circumferentially spaced about the downstream end of the compressor.
Generally, a gas turbine engine operates as follows. Rotor blades in the compressor rotate about the shaft to compress a flow of air. The supply of compressed air is split and directed to the individual combustion cans, within which the supply of compressed air is used to combust a supply of fuel. The resulting flow of hot gases from the combustion exits the combustion cans and is directed into the turbine, where the pressurized flow is expanded. The expansion through the turbine induces the turbine rotor blades to rotate about the shaft. In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating turbine rotor blades, which may be used to rotate the rotor blades of the compressor, thus producing the flow of compressed air, and the coils of a generator to generate electricity. During operation, because of the extreme temperatures, the velocity of the working fluid, and, for the rotor blades, the rotational velocity of the rotating parts, the airfoils through both the compressor and the turbine are highly stressed parts. As a result, in general, reducing the thermal load on the airfoils in the turbine is a continuing objective.
To reduce the thermal load, cooling air is extracted from the compressor and passed through cooling channels that are formed within the rotor and stator blades. After passing through the cooling channels of the airfoils, the cooling air generally is dumped back into the main flow through the turbine. However, the cooling air has a negative impact on the efficiency of the engine. Therefore, the amount of cooling air used to cool the turbine airfoils in this manner should, to the extent possible, be minimized.
In most industrial gas turbine engines, cooling air is also used to cool the combustion cans and transition pieces of the combustor assembly. Typically, air is taken from the compressor and passed through the gaps between the individual cans. After passing between the combustion cans, any flow not utilized in the combustion process is dumped back into the main flow. This generally takes place at the beginning of the turbine section of the engine and just upstream of the row of stator blades in the first stage. More particularly, the transition piece aft frame cooling air reenters the main flow at discrete circumferential locations defined by the area between two neighboring combustion cans. However, conventional gas turbine design does not fully utilize the capacity of this air to cool the stator blades in the leading stages of the turbine. Given that it is often the inability of present materials to withstand higher firing temperatures that prevents more efficient gas turbine engines from being constructed, new methods of operation, apparatus and/or assemblies that more fully utilize this type of compressor supplied cooling air would be greatly desired. Further, new methods of operation, apparatus and/or gas turbine assemblies that minimize the amount of cooling air bled from the compressor to pass through the airfoils and dumped back into the main flow of the working fluid would increase turbine engine efficiency and, thus, also be desired.